INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Meanwhile, an insidious supervillain (Kenneth Branagh) lurks, threatening to take Crown down. — Mya Copeland, Variety, 29 July 2026 But there’s a historical, and some might argue insidious, irony to all of this. — Drew Pittock, USA Today, 25 July 2026 But, as Ellis demonstrates in this survey of the city’s racial history, liberal policy achievements tend to obscure more insidious forms of exclusion. — The New Yorker, New Yorker, 20 July 2026 Beneath all the splendor, the couture, the balls, and the opera lurked an undercurrent of hatred, one that would fester and erupt in ways both insidious and catastrophic. — Literary Hub, 17 July 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

And with most of the original cast now long gone, the latest sequel often feels as cursed as that treacherous netherworld.

— Los Angeles Times, Los Angeles Times, 21 Aug. 2026
The first season concludes with the revelation that Mizu’s ambitions of vengeance require her to travel to London — a treacherous journey by sea, as briefly shown in the second season trailer.

— Jess Weatherbed, The Verge, 21 Aug. 2026

Definition of treacherous

Adjective

Clinicians found real value in cases involving subtle fractures in the knees, feet and other extremities, where conventional X-ray findings were inconclusive or missed the fracture altogether.

— Erez Meltzer, Forbes.com, 21 Aug. 2026
Then there are the subtle vanilla notes like those found in Orb Oils’s Lenny fragrance, matcha in Le Labo’s, or, say, Flamingo Estate’s Prinsesstårta roll-on captures notes of marzipan like a slice of Sant Ambroeus Princess cake.

— Arden Fanning Andrews, Vogue, 21 Aug. 2026

Definition of subtle

Adjective

Meta will be subject to an injunction prohibiting it from making further false, misleading, or deceptive statements around its safety features.

— Jill Goldsmith, Deadline, 26 Aug. 2026
The agency has said deceptive or unfair data practices can violate existing consumer protection laws.

— Kurt Knutsson, FOXNews.com, 24 Aug. 2026

Definition of deceptive

Adjective

Another false dawn was Manchester City’s bright start in a 2-0 win over Chelsea, without the man who had just been named player of the tournament at Euro 2024, Rodri.

— Michael Cox, New York Times, 26 Aug. 2026
In turn, Baldoni and Wayfarer Studios filed a defamation suit, which claimed Lively and her husband, Ryan Reynolds, had planted false claims in order to take over creative control of the film.

— Caitlin Huston, HollywoodReporter, 26 Aug. 2026

Definition of false

Adjective

That’s misleading, the FTC said, since customers who know how prices are set could take defensive measures, such as using a private browsing session or a virtual private network to mask their browsing history.

— Ashley Belanger, ArsTechnica, 21 Aug. 2026
There are plenty of well-meaning people and experts posting content everyday, but both professors noted that even that material may be misleading, inconclusive or overly generalized.

— Carlos De Loera, Los Angeles Times, 21 Aug. 2026

Definition of misleading

Adjective

Bogus texts, mystery calls, deceitful emails all aimed at stealing your personal information and your money are relentless.

— Donna Vickroy, Chicago Tribune, 13 Aug. 2026
The mutual trust and goodwill that xenia sought to cultivate has been eroded by this one deceitful act, creating a world that is defined by this moral violation.

— Brianna Zigler, Entertainment Weekly, 19 July 2026

Definition of deceitful

Adjective

In between some of the manager’s more clip-worthy quotes, there were more of his usual — and not incorrect — platitudes.

— Cody Stavenhagen, New York Times, 25 Aug. 2026
Mosseri said the plaintiff lawyers are incorrect in suggesting that Meta also reduced the number of researchers studying youth mental health harms after Haugen’s leaks.

— Jonathan Vanian, CNBC, 25 Aug. 2026

Definition of incorrect

Browse Nearby Words

inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 28 Aug. 2026.

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Synonyms of insidious

adjective

Example Sentences

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